Chronotypes and circadian rhythms in university students.

Inter-individual differences have been described in circadian timing organization, including the characteristics of phase preferences known as chronotypes. Social, biological and geophysical factors can influence the characteristics of morning-evening preference. Although morning individuals report inability to return to sleep after waking up and difficulties in maintaining nocturnal sleep most complaints are reported by evening individuals. The objective of the present study was to analyze the temporal organization of chronotypes at different phases. We measured the rhythms of activity/rest, sleep/wake, wrist temperature, attention and cycles of exposure to light of 32 university volunteers over 21 consecutive days of data collection. The acrophases of the analyzed rhythms correlate with the score of Horne & Östberg Questionnaire, but not the parameters of the cycle of exposure to light. The evening type volunteers who have morning classes showed no corresponding phase advanced of the rhythms, social jet lag and disruption in the rhythm of attention, suggesting difficulty to entrainment by the university schedules. [ABSTRACT FROM AUTHOR]